<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <script src="/js/vue.js"></script>
</head>
<body>
  <div id="app">
      <p>First name:<input type="text" v-model="firstName"></p>
      <p>Last name:<input type="text" v-model="lastName"></p>
      <p>fullname:{{fullname}}</p>
      <button @click="change">改变fullname</button>
  </div>
<br>
  <script>
   let app = new Vue({
   el:"#app",
   data:{ 
     firstName:"",
     lastName:""
      },
      methods: {
        change(){
            this.fullname='Harry Potter'
        }
      },
      computed:{
        fullname:{
            get:function(){
                return this.firstName+''+this.lastName;
            },
            set:function(){
                var arr = newVal.split('');
                this.firstName=arr[0];
                this.lastName=arr[1];
            }
        }
      }
    })
  </script>
</body>
</html>